#include<stdio.h>
#include<string.h>

int main(0{
    int n, dq[1000], front = 500, rear = 500;
    scanf("%d", &n);
    while (n--){
        char cmd[20];
        scanf("%s", cmd);
        
        if(strcmp(cmd, "priority_board")==0){
            int x; scanf("%d", &x);
            dq[--front] = x;
        }
        else if (strcmp(cmd, "general_board")==0){
            int x; scanf("%d", &x);
            dq[rear++] = x;
        }
        else if (strcmp(cmd, "board_train")==0)
        {
            if (front == rear)printf("Invalid operation\n");
            else front++;
        }
        else if (strcmp(cmd, "display")==0){
            if (front == rear) printf("No passengers\n");
            else {
                for (int i=front;i<rear;i++){
                    printf("%d", dq[i]);
                    if (i<rear-1)printf(" ");
                }
                printf("\n");
            }
        }
    }
    return 0;
    }
})